Capecitabine Plus Pyrotinib Versus Capecitabine Plus Trastuzumab and Pertuzumab in the First-line Treatment of HER2-positive Metastatic Breast Cancer

Inclusion Criteria: * HER2 positive recurrent or metastasis breast cancer. * Patients with measurable disease are eligible. * Eastern Cooperative Oncology Group(ECOG) performance status 0 or 1. * Adequate organ function. * Signed, written inform consent obtained prior to any study procedure. Exclusion Criteria: * History of anti-cancer therapy for MBC（with the exception of one prior hormonal regimen for MBC）. * History of HER tyrosine kinase inhibitors or monoclonal antibody for breast cancer in any treatment setting，except trastuzumab used in the neo-adjuvant or adjuvant setting. * Assessed by the investigator to be unable receive systemic chemotherapy. * History of other malignancy within the last 5 years，except for carcinoma in situ of cervix，basal cell carcinoma or squamous cell carcinoma of the skin that has been previously treated with curative intent. * Pregnant or lactating women，or for women of childbearing potential unwilling to use a highly-effective contraception during of the study treatment and for at least 7 months after the last dose of study treatment.